Although the mechanisms responsible for neurologic dysfunction in AIDS Dementia Complex (ADC) are poorly understood, HIV infection of microglia and brain macrophage seems to play a central role. Not all macrophage- tropic variants appear to be neuropathic, however. Macrophage-tropic strains can be isolated from the majority of infected individuals, viral invasion of the CNS occurs commonly, and virus can frequently be identified in the CNS. Yet only some individuals develop encephalopathy. Additional determinants may include host factors such as immune responses, co-infections, or viral strain differences. Our hypothesis is that macrophage-tropic strains of HIV-1 vary in their neuropathic properties, such as the ability to productively or non-productively infect CNS cells or to induce neurotoxic effects, and that these differences are responsible, in part, for the development of encephalopathy. The aim of this study is to better understand the viral strain variations which cause certain macrophage-tropic strain to be neuropathic, and contribute to the development of neurologic dysfunction. First, we will determine whether primary isolates derived from brain and other sites of individuals with and without encephalopathy differ in their interaction with primary CNS cells. We will generate a panel of primary isolates from a few individuals with and without ADC and test their ability to productively replicate in microglia or establish restricted infection in other primary glial and in neuronal cells. Second, we will examine differences among macrophage-tropic viruses in their ability to induce potentially neuropathic effects. We will compare the ability of these primary isolates to elicit macrophage cytokine secretion, induced neurotoxic effects in macrophage-neuron coculture, or establish restricted infection in and/or directly alter neuronal function. Third, we will define the viral genetic basis among macrophage-tropic strains for these biological differences. We will generate biologically active molecular clones of several of these primary isolates with relevant biological differences, which will be used to map the basis for these characteristics. In addition, we will construct chimeric viruses using PCR-amplified fragments generated directly from selected regions of brain which exhibit particular pathologic manifestations. Because macrophage-tropic strains appear to be necessary but not sufficient for the development of ADC, it is critical to better understand the characteristics of neuropathic variants. We will address these questions in the context of this Program utilizing primary isolates from tissue provided by the Neuropathology Core, which allows for close correlation between viral phenotype and histopathological changes in vivo, primary human brain cultures and differentiated neuronal cells provided by Program I as target for infection, and methods for detection and analysis of restricted infection offered by the Molecular Neurovirology Core.